1. Field of the Invention
The present invention relates to an exhaust controlling device of a direct cylinder fuel-injected spark-ignition engine.
2. Description of the Related Art
A related engine controlling device is available including an adjustable valve mechanism capable of adjusting a valve characteristic (e.g., valve timing or valve opening angle or valve lift) requested during stratified combustion to be different from a valve characteristic requested during homogeneous combustion. Homogeneous combustion is a combustion state or method preferred for normal operation of a four-stroke spark-ignition engine, while stratified combustion is a combustion state or method preferred during cold startup of the engine to enable quick heating of the catalytic converter for improving startup exhaust emissions performance of the engine. In many cases, homogenous combustion and stratified combustion require different valve characteristics. When a request is detected to be present to switch from homogeneous combustion to stratified combustion, a request for changing the valve characteristic may be made at the same time. In such a case, when the switching of the combustion state, and the changing of the valve characteristic are performed at the same time, a combustion state becomes unstable, as a result of which a switching shock may occur. Therefore, the prior art resolves this problem by switching the combustion state changing the valve characteristic.
When an engine is cold, the combustion method may be switched to stratified combustion, which excels in exhaust performance during the period shortly after starting the engine (i.e., while the exhaust piping and catalytic converter are cold) compared with homogeneous combustion. However, in the aforementioned related engine controlling device of the prior art, even in such a case, the combustion method is switched after changing the valve characteristic. Therefore, the switching of the combustion method is delayed, thereby deteriorating the exhaust performance.